This invention relates generally to rotary valve assemblies of the type used in a reciprocating combustion engine to regulate flow of gasses through engine valve passages. More particularly, this invention relates to an improved rotary valve assembly designed for variable valve timing during engine operation, in response to different engine operating conditions.
Reciprocating combustion engine are well known in the art to include one or more pistons mounted on a rotating crankshaft for reciprocal displacement within one or more combustion cylinders. Reciprocal movement of the piston within each cylinder is accompanied by a timed sequence delivery of a gaseous fuel-air mixture to the cylinder via an intake passage, and subsequent discharge of combustion products from the cylinder through an exhaust passage. Intake and exhaust valves are provided to open and close the intake and exhaust passages in precision coordination with piston movement.
In the past, intake and exhaust valves for internal combustion engines have been provided in different forms. As one example, piston-type poppet valves are used extensively in a wide variety of combustion engines, wherein spring-loaded valves are mechanically linked to the engine crankshaft for timed displacement to open and close the associated engine valve passages. Rotary valve plates having open arcuate valve ports have also been used, wherein the rotary valve plates are also linked mechanically to the engine crankshaft for coordinated displacement in relation to piston reciprocation within the associated cylinder. In some engines, particularly such as two-stroke engines, reed-type valves responsive to pressure fluctuations within the crankcase have been used. In most valve designs, adjustment of valve timing during normal engine operation, and in response to different selected engine operating conditions, has either not been possible or has otherwise required complex and costly valve mechanisms and related timing control systems.
In some combustion engines, variable valve timing can be extremely desirable for purposes of optimizing engine power output and minimizing toxic emissions over a broad range of engine operating conditions. For example, small two-stroke combustion engines are used in a wide variety of relatively low power applications, such as in motorcycles and scooters and in lawn and garden implements such as mowers, trimmers, blowers, mulchers, and the like. Such combustion engines are typically designed with relatively simple and thus inexpensive intake and exhaust valve mechanisms aimed at providing a desired balance of power output and emissions characteristics. However, variable valve timing in such engines, particularly intake valve timing as a function of engine speed and/or load, has been generally impractical and in most instances not possible. As a result, small combustion engines of this type are normally designed for relatively efficient operation with a narrow range of engine speed and/or load. Unfortunately, when the engine is operated outside this narrow design range, relatively inefficient engine performance and/or a substantial increase in undesired emissions tends to result.
There exists, therefore, a significant need for improvements in valve assemblies used with combustion engines, particularly with respect to a relatively simple valve mechanism adapted for adjustable valve timing during engine operation in relation to selected engine characteristics such as speed and/or load. The present invention fulfills these needs and provides further related advantages.